Service Providers that use RSVP-TE Label Switched Paths (LSPs) typically uses some form of protection mechanism for protecting the LSPs from any un-expected failures. The most common way of LSP protection is Fast Re-Route (FRR). But the above protection approaches protects the LSP with only single failure, i.e. if the RSVP Tunnel discovers a failure it will commence using the FRR (Backup) Path to make sure it stays up and service is not disrupted. MPLS Fast Reroute (also called MPLS local restoration or MPLS local protection) is a local restoration network resiliency mechanism. It is a feature of RSVP Traffic Engineering (RSVP-TE).
Referring to FIG. 1a there may be seen an exemplary network having six MPLS Label Switch Routers PE1 101, PE2 102, PE3 103, PE4 104, PE5 105, and PE6 106. Each of the Label Switch Routers has a facility linking them to other Label Switch Routers in the exemplary network. Thus facility 112 links Label Switch Routers 101 and 102; facility 113 links Label Switch Routers 101 and 103; facility 123 links Label Switch Routers 102 and 103; facility 124 links Label Switch Routers 102 and 104; facility 125 links Label Switch Routers 102 and 105; facility 135 links Label Switch Routers 103 and 105; facility 145 links Label Switch Routers 104 and 105; facility 146 links Label Switch Routers 104 and 106; and facility 156 links Label Switch Routers 105 and 106.
In FIG. 1a Label Switched Path 180 may be seen connecting PE1 101 to PE6 106 while traversing network nodes PE2 102 and PE5 105. In MPLS local protection each LSP passing through a facility is protected by a Backup path which originates at the node immediately upstream to that facility. This node which redirects the traffic onto the preset Backup path is called the Point of Local Repair (PLR), and the node where a Backup LSP merges with the primary LSP is called Merge Point (MP). In FIG. 1a facility 125 has PE2 102 as its Point of Local Repair, and PE5 105 as its Merge Point. Bypass LSP 181 provides a Bypass LSP around facility 125.
This mechanism (local protection) provides faster recovery because the decision of recovery is strictly local. By way of comparison, when recovery mechanisms are employed at the IP layer, restoration may take several seconds which is unacceptable for real-time applications (such as VoIP). In contrast, MPLS local protection meets the requirements of real-time applications with recovery times comparable to those of SONET rings (<50 ms).
Referring to FIG. 1b, the use of Backup LSP 181 is illustrated. In FIG. 1b, the exemplary network of FIG. 1a has suffered a fault 190 to facility 125, thus interrupting LSP 180. The local protection mechanism operates to provide Bypass LSP 181 around the fault at facility 125, thus allowing continuity of service.
However, this method of protection operates to protect against single faults. In the event of a scenario where an LSP is already been protected by a Bypass LSP (FRR), and there is a second failure in the network which causes the FRR/Bypass LSP also to go down, the whole LSP would go down. The service originally supported by the LSP is disrupted. For example, in reference to FIG. 1b, were there the presence of the first fault 190, and then the occurrence of a second fault on facility 135, then both primary and Bypass LSPs would be broken. The MPLS Fast Reroute standard does not address the double failure scenario.